import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

class Message {
    public String from;
    public String to;
    public String message;
}
@WebServlet("/message")
public class MessageServlet extends HttpServlet {
    private ObjectMapper objectMapper=new ObjectMapper();

    private List<Message> messages=new ArrayList<>();
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理提交消息的请求
       Message message= objectMapper.readValue(req.getInputStream(),Message.class);
      //最简单的保存方法是保存到内存中
       messages.add(message);
       //通过ContentType告知页面，返回的数据是json格式
       resp.setContentType("application/json;charset=utf8");
       resp.getWriter().write("{\"ok\":true}");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取到消息列表，只要把消息列表内容整个给返回客户端即可
        //此处需要使用objectMapper把Java对象，转成json格式字符串

        String jsonString=objectMapper.writeValueAsString(messages);
        System.out.println("jsonString: " + jsonString);
        resp.setContentType("application/json;charset=utf8");
        resp.getWriter().write(jsonString);
    }


}
